Down syndrome occurs when a baby develops an extra copy of the 21st chromosome during pregnancy, resulting in telltale symptoms. These distinctive signs and symptoms can include recognizable facial features, in addition to developmental and intellectual difficulties.

Interested to learn more? We’ve compiled some facts and statistics about Down syndrome below.

Each year, about 6,000 babies are born with Down syndrome in the United States

One out of every 700 babies born in the United States is estimated to have the condition.

The estimated incidence of Down syndrome is between 1 in 1,000 to 1 in 1,100 live births worldwide, according to the World Health Organization.

Down syndrome is the most common chromosomal disorder in the United States

Though Down syndrome is the most commonly occurring genetic chromosomal disorder, the way the condition presents itself in each person will differ.

Some people will have mild to moderate intellectual and developmental problems, while others might have more severe complications.

The same goes for health, where some people with Down syndrome may be healthy, while others could have a variety of health-related complications, such as heart defects.

Three different types of Down syndrome exist

While the condition may be thought of as a singular syndrome, there are actually three different types.

Trisomy 21, or nondisjunction, is the most common. It accounts for 95 percent of all cases.

The other two types are called translocation and mosaicism. Regardless of which type a person has, everyone with Down syndrome has an extra pair of chromosome 21.

Babies of every race can have Down syndrome

Down syndrome does not occur in one race more than another.

In the United States, however, black or African American infants with Down syndrome have a lower chance of surviving beyond their first year of life compared with white infants with the condition, according to the CDC. The reasons why are not clear.

People with Down syndrome have an extra chromosome

The nucleus of a typical cell contains 23 pairs of chromosomes, or 46 total chromosomes. Each of these chromosomes determines something about you, from your hair color to your sex.

People with Down syndrome have an extra copy or partial copy of chromosome 21.

Maternal age is the only certain risk factor for Down syndrome

Eighty percent of children with either trisomy 21 or mosaicism Down syndrome are born to mothers who are younger than 35 years old. Younger women have babies more frequently, so the number of babies with Down syndrome are higher in that group.

However, moms who are older than 35 are more likely to have a baby affected by the condition.

According to the National Down Syndrome Society, a 35-year-old woman has approximately a 1 in 350 chance of conceiving a child with Down syndrome. This chance increases gradually to 1 in 100 by age 40 and approximately 1 in 30 by age 45.

Down syndrome is a genetic condition, but it isn’t hereditary

Neither trisomy 21 nor mosaicism is inherited from a parent. These cases of Down syndrome are the result of a random cell division event during the baby’s development.

But one-third of translocation cases are hereditary, accounting for about 1 percent of all cases of Down syndrome. That means the genetic material that can lead to Down syndrome is passed from parent to child.

Both parents can be carriers of the translocation Down syndrome genes without showing any signs or symptoms of Down syndrome.

Women who have had one child with Down syndrome have an increased chance of having another child with the condition

If a woman has one child with the condition, her risk for having a second child with the syndrome is about 1 in 100 up until age 40.

The risk of having a second child with the translocation type of Down syndrome is about 10 to 15 percent if the mother carries the genes. If the father is the carrier, however, the risk is about 3 percent.

People with Down syndrome can have a variety of complications

Infants with Down syndrome who also had a congenital heart defect were found to be five times more likely to die in the first year of life compared to infants with Down syndrome who didn’t have a heart defect.

Likewise, a congenital heart defect is one of the greatest predictors of death before age 20. New developments in heart surgery, however, are helping people with the condition live longer.

Compared to children without Down syndrome, children with Down syndrome are at higher risk for complications that include hearing loss — up to 75 percent may be affected — and eye diseases, like cataracts — up to 60 percent.

Symptoms of Down syndrome aren’t the same for each person

Down syndrome causes many distinct characteristics, like:

  • a small stature
  • upwardly slanting eyes
  • a flattened bridge of the nose
  • a short neck

However, each person will have different degrees of the characteristics, and some of the features may not appear at all.

People with Down syndrome can work but often have jobs that underutilize their skills

According to one national survey in 2015, only 57 percent of adults with Down syndrome were employed, and only 3 percent were full-time paid employees.

More than 25 percent of respondents were volunteers, almost 3 percent were self-employed, and 30 percent were unemployed.

Moreover, the highest percentage of people worked in the restaurant or food industry and in janitorial and cleaning services, even though a large majority of adults reported that they use computers.

The number of infants born with Down syndrome who die before their first birthday is falling

From 1979 to 2003, the rate of death for a person born with Down syndrome during their first year of life fell by about 41 percent.

That means only about 5 percent of babies born with Down syndrome will die by age 1.

The average age of survival continues to increase

At the turn of the 20th century, children with Down syndrome rarely lived past 9 years old. Now, thanks to advancements in treatment, the majority of people with the condition will live to age 60. Some may live even longer.

Early intervention is vital

While Down syndrome can’t be cured, treatment and teaching life skills can go a long way to improve the child’s — and eventually the adult’s — quality of life.

Treatment programs often include physical, speech, and occupational therapies, life skills classes, and educational opportunities. Many schools and foundations offer highly specialized classes and programs for children and adults with Down syndrome.

Half of older adults with Down syndrome will develop memory loss

People with Down syndrome are living to be much older, but as they age, it’s not uncommon for them to develop thinking and memory problems.

According to the Down’s Syndrome Association, by their 50s, approximately half of the people with Down syndrome will be showing evidence of memory loss and other problems — such as loss of skills — associated with having Alzheimer’s disease.

While Down syndrome remains the most common chromosomal disorder that children are born with in the United States today, the future is getting brighter for them.

People with the condition are prospering, and their lifespans are increasing thanks to the improvement of treatments and therapies.

Moreover, an increase in understanding of the preventive measures and complications associated with the condition are allowing caregivers, educators, and doctors to anticipate and plan for a longer future.

Jen Thomas is a journalist and media strategist based in San Francisco. When she’s not dreaming of new places to visit and photograph, she can be found around the Bay Area struggling to wrangle her blind Jack Russell terrier or looking lost because she insists on walking everywhere. Jen is also a competitive Ultimate Frisbee player, a decent rock climber, a lapsed runner, and an aspiring aerial performer.